Foreword........................................................................

1 Scope......................................................................

2 References...................................................................

3 Definitions, symbols and abbreviations..............................................

3.1 Definitions.................................................................

3.2 Symbols...................................................................

3.3 Abbreviations...............................................................

4 Non-Terrestrial Networks Overview – background information.............................

4.1 Roles for Non-Terrestrial Networks in 5G system........................................

4.2 5G Use Cases wherein Non-Terrestrial Network components have a role........................

4.2.1 5G use cases introduction.....................................................

4.3 Satellite and aerial access network architecture principles..................................

4.4 Characteristics of NTN Terminals for satellite / aerial access network..........................

4.5 Air/Space borne vehicle characteristics..............................................

4.6 Coverage pattern of NTN.......................................................

4.7 Non-Terrestrial Network architecture options..........................................

4.8 Spectrum..................................................................

5 Non-Terrestrial Networks deployment scenarios........................................

5.1 Scenarios overview...........................................................

5.2 Attributes..................................................................

5.3 Doppler and Propagation delay characterisation.........................................

5.3.1 Methodology.............................................................

5.3.1.1 Propagation delay........................................................

5.3.1.2 Differential delay........................................................

5.3.1.3 Doppler shift/variation.....................................................

5.3.2 Geo-stationary platforms.....................................................

5.3.2.1 Propagation delay

5.3.2.2 Differential delay

5.3.2.3 Doppler shift

5.3.3 Aerial vehicle.............................................................

5.3.4 Non geostationary satellites....................................................

5.3.4.1 Propagation delay

5.3.4.2 Differential delay

5.3.4.3 Doppler Shift and variation rate

5.3.4.3.1 Case at 2 GHz

5.3.4.3.2 Case in Ka band

5.3.4.4 Doppler Shift and variation rate

5.3.5 Synthesis for each scenarios...................................................

6 Non-Terrestrial Networks channel models............................................

6.1. Status/expectation of existing information for satellite/HAPS channels..........................

6.1.1 Channel modeling works outside of 3GPP..........................................

6.1.2 Targeted user environment....................................................

6.1.3 Modeling objectives........................................................

6.2 Differences between satellite/HAPS and cellular channel modelling............................

6.3 Coordinate system............................................................

6.4 Antenna modelling

6.4.1 HAPS/Satellite antenna

6.4.2 UE antenna pattern.........................................................

6.5 Methodology to define channel models..............................................

6.5.1 System-level methodology....................................................

6.5.2 Link-level methodology......................................................

6.6 Large scale model............................................................

6.6.1 LOS probability...........................................................

6.6.2 Path loss and Shadow fading...................................................

6.6.3 O2I penetration loss.........................................................

6.6.4 Atmospheric absorption......................................................

6.6.5 Rain and cloud attenuation....................................................

6.6.6 Scintillation..............................................................

6.6.6.1 Ionospheric scintillation

6.6.6.1.1 Ionospheric scintillation indices............................................

6.6.6.1.2 Ionospheric scintillation location dependence...................................

6.6.6.1.3 Frequency scaling.....................................................

6.6.6.1.4 Model for Ionospheric scintillation loss.......................................

6.6.6.2 Tropospheric scintillation

6.6.6.2.1 Model for Tropospheric scintillation loss......................................

6.7 Fast fading model............................................................

6.7.1 Flat fading...............................................................

6.7.2 Frequency selective fading....................................................

6.8. Additional modelling components..................................................

6.8.1 Time-varying Doppler shift....................................................

6.8.2 Faraday rotation...........................................................

6.9 Channel models for link level simulations.............................................

6.9.1 CDL models..............................................................

6.9.2 TDL models..............................................................

6.10 Channel model calibration.......................................................

6.10.1 NTN channel model features per deployment scenarios.................................

7 Potential key impact areas on NR to support NTN......................................

7.1 Specific constraints associated to NTN...............................................

7.2 NR features/protocols potentially affected.............................................

7.3 NR modifications to support the Non-Terrestrial Network deployment scenarios...................

7.3.1 Methodology.............................................................

7.3.2 Motion of the space/aerial vehicles...............................................

7.3.2.1 Hand-Over and paging.....................................................

7.3.2.1.1 Problem statement.....................................................

7.3.2.1.2 Assessment of conditions for NR operation in Non-Terrestrial networks..................

7.3.2.1.3 NR impact considerations................................................

7.3.2.2 TA adjustment..........................................................

7.3.2.2.1 Problem statement.....................................................

7.3.2.2.2 Assessment of conditions for NR operation in Non-Terrestrial networks..................

7.3.2.2.3 NR impact considerations................................................

7.3.2.3 Initial synchronization in downlink............................................

7.3.2.3.1 Problem statement.....................................................

7.3.2.3.2 Assessment of conditions for NR operation in Non-Terrestrial networks..................

7.3.2.3.3 NR impact considerations................................................

7.3.2.4 DMRS time density......................................................

7.3.2.4.1 Problem statement.....................................................

7.3.2.4.2 Assessment of conditions for NR operation in Non-Terrestrial networks..................

7.3.2.4.3 NR impact considerations................................................

7.3.3 Altitude of the space/aerial vehicles..............................................

7.3.3.1 HARQ...............................................................

7.3.3.1.1 Problem statement

7.3.3.1.2 Assessment of conditions for NR operation in non-terrestrial networks

7.3.3.1.3 NR impact considerations

7.3.3.2 MAC/RLC procedures.....................................................

7.3.3.2.1 Problem statement.....................................................

7.3.3.2.2 Assessment of conditions for NR operation in Non-Terrestrial networks..................

7.3.3.2.3 NR impact considerations................................................

7.3.3.3 Physical layer procedures (ACM, power control)...................................

7.3.3.3.1 Problem statement.....................................................

7.3.3.3.2 Assessment of conditions for NR operation in Non-Terrestrial networks..................

7.3.3.3.3 NR impact considerations................................................

7.3.4 Cell size (Beam foot print)....................................................

7.3.4.1 PRACH and Random access.................................................

7.3.4.1.1 Problem statement.....................................................

7.3.4.1.2 Assessment of conditions for NR operation in Non-Terrestrial networks

7.3.4.1.3 NR impact considerations

7.3.4.2 TA in Random access response message.........................................

7.3.4.2.1 Problem statement.....................................................

7.3.4.2.2 Assessment of conditions for NR operation in Non-Terrestrial networks..................

7.3.4.2.3 NR impact considerations................................................

7.3.5 Propagation channel........................................................

7.3.5.1 DMRS frequency density...................................................

7.3.5.1.1 Problem statement.....................................................

7.3.5.1.2 Assessment of conditions for NR operation in Non-Terrestrial networks..................

7.3.5.1.3 NR impact considerations................................................

7.3.5.2 Cyclic prefix...........................................................

7.3.5.2.1 Problem statement.....................................................

7.3.5.2.2 Assessment of conditions for NR operation in Non-Terrestrial networks..................

7.3.5.2.3 NR impact considerations................................................

7.3.6 Duplex mode

7.3.6.1 FDD/TDD Duplexing mode

7.3.6.1.1 Problem statement.....................................................

7.3.6.1.2 Assessment of conditions for NR operation in Non-Terrestrial networks..................

7.3.6.1.3 NR impact considerations................................................

7.3.7 Satellite or aerial Payload performance............................................

7.3.7.1 PT-RS...............................................................

7.3.7.1.1 Problem statement.....................................................

7.3.7.1.2 Assessment of conditions for NR operation in Non-Terrestrial networks..................

7.3.7.1.3 NR impact considerations................................................

7.3.7.2 PAPR................................................................

7.3.7.2.1 Problem statement.....................................................

7.3.7.2.2 Assessment of conditions for NR operation in Non-Terrestrial networks..................

7.3.7.2.3 NR impact considerations................................................

7.3.8 Network architecture........................................................

7.3.8.1 Protocols.............................................................

7.3.8.1.1 Problem statement.....................................................

7.3.8.1.2 Assessment of conditions for NR operation in Non-Terrestrial Networks.................

7.3.8.1.3 NR impact considerations................................................

8 Recommendations on the way forward..............................................

8.1 General outcomes

8.2 Reference deployment scenarios

8.3 Non-Terrestrial network channel modelling

8.4 NR impacts to support Non-Terrestrial networks

8.4.1 Type of potential NR impacts..................................................

8.4.2 Assessment of potential NR impacts to support Non-Terrestrial networks......................

Annex A: Example of reference scenario for calibration of large scale parameters............

Annex B: Non Terrestrial network characteristics.....................................

B.1 NTN Phase noise masks.........................................................

Annex C: Change History.......................................................

This Technical Report has been produced by the 3rd Generation Partnership Project (3GPP).

The contents of the present document are subject to continuing work within the TSG and may change following formal TSG approval. Should the TSG modify the contents of the present document, it will be re-released by the TSG with an identifying change of release date and an increase in version number as follows:

Version x.y.z

where:

x the first digit:

1 presented to TSG for information;

2 presented to TSG for approval;

3 or greater indicates TSG approved document under change control.

y the second digit is incremented for all changes of substance, i.e. technical enhancements, corrections, updates, etc.

z the third digit is incremented when editorial only changes have been incorporated in the document.

This technical report is related to a study item New Radio to support Non-Terrestrial Networks. The purpose of this TR is to collect the TSG RAN and RAN WG1 findings related to the study.

The objectives for the study are the following

- Definition of the Non-Terrestrial Networks deployment scenarios and related system parameters such as architecture, altitude, orbit etc.

- Adaptation of the 3GPP channel models for non-terrestrial networks (propagation conditions, mobility, …).

- For the described deployment scenarios, identification of any key impact areas on the New Radio interface that may need further evaluations.

The following documents contain provisions which, through reference in this text, constitute provisions of the present document.

- References are either specific (identified by date of publication, edition number, version number, etc.) or non‑specific.

- For a specific reference, subsequent revisions do not apply.

- For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document.

[1] 3GPP TR 21.905: "Vocabulary for 3GPP Specifications".

[2] 3GPP TS 36.101: "Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) radio transmission and reception (Release 14)".

[3] 3GPP TR 38.801: "Technical Specification Group Radio Access Network; Study on new radio access technology: Radio access architecture and interfaces (Release 14)".

[4] 3GPP TR 38.804: "Technical Specification Group Radio Access Network; Study on New Radio Access Technology; Radio Interface Protocol Aspects (Release 14)".

[5] 3GPP TR 38.913: "Study on Scenarios and Requirements for Next Generation Access Technologies (Release 14)".

[6] 3GPP TS 22.261: "Service requirements for next generation new services and markets".

[7] A. Guidotti et. al, "Satellite-enabled LTE systems in LEO Constellations", 2017 IEEE International Conference on Communications (ICC), Paris, May 2017, pp. 876-881, doi: 10.1109/ICCW.2017.7962769

[8] 3GPP TR 38.802 v14.1.0, "Study on New Radio Access Technology Physical Layer Aspects (Release 14)".

[9] Void

[10] Recommendation ITU-R P.681-10, "Propagation data required for the design of earth-space land mobile telecommunication systems", Dec. 2017.

[11] Recommendation ITU-R P.618-13, "Propagation data and prediction methods required for the design of Earth-space telecommunication systems", Dec. 2017.

[12] 3GPP TR 38.901: "Study on channel model for frequencies from 0.5 to 100 GHz (Release 14)".

[13] Recommendation ITU-R P.531-13, "Ionospheric propagation data and prediction methods required for the design of satellite services and systems", September 2016.

[14] Wheelon, A.D., Electromagnetic Scintillation II. Weak Scattering, Cambridge Univ. Press, pp. 110-111, Cambridge, U.K., 2005.

[15] F. P. Fontan, M. Vazquez-Castro, C. E. Cabado, J. P. Garcia and E. Kubista, "Statistical modeling of the LMS channel," in IEEE Transactions on Vehicular Technology, vol. 50, no. 6, pp. 1549-1567, Nov 2001

[16] A. Jahn and E. Lutz, "Propagation Data and channel model for LMS systems", Final Rep. ESA PO 141 742. DLR, 1995.

[17] Prieto-Cerdeira, R., Perez-Fontan, F., Burzigotti, P., Bolea-Alamañac, A. and Sanchez-Lago, I., "Versatile two-state land mobile satellite channel model with first application to DVB-SH analysis", Int. J. Satell. Commun. Network., 28: 291–315., June 2010.

[18] Void

[19] Void

[20] 3GPP TS 38.321 "Technical Specification Group Radio Access Network; NR; Medium Access Control (MAC) protocol specification (Release 15)".

[21] 3GPP TS 38.211, "Technical Specification Group Radio Access Network; NR; Physical channels and modulation (Release 15)".

[22] 3GPP TS 38.133 "Technical Specification Group Radio Access Network; NR; Requirements for support of radio resource management (Release 15)".

[23] 3GPP TS 38.214, "Technical Specification Group Radio Access Network; NR; Physical layer procedures for data (Release 15)".

[24] 3GPP TR 38.802 v14.1.0, "Study on New Radio Access Technology Physical Layer Aspects (Release 14)", June 2016.

[25] 3GPP TS 36.101: "Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) radio transmission and reception (Release 14)".

[26] 3GPP TS 38.101, "Technical Specification Group Radio Access Network; NR; User Equipment (UE) radio transmission and reception".

[27] 3GPP TS 36.104, "Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Base Station (BS) radio transmission and reception".

[28] O. Kodheli, A. Guidotti, and A. Vanelli-Coralli. "Integration of Satellites in 5G through LEO Constellations", CoRR abs/1706.06013 (2017): pp. 1-6

[29] 3GPP TS 36.321, "Evolved Universal Terrestrial Radio Access (E-UTRA); Medium Access Control (MAC) protocol specification (Release 15)", v1.0.0 (2017-12).

[30] R1-1802632, "Considerations on random access for non-terrestrial networks", Interdigital Inc., 3GPP TSG RAN WG1 Meeting #93, Busan, Korea, May 21st – 25th, 2018.

[31] R1-1804236, "Discussion on the NR impacts on random access for NTN", ZTE, 3GPP TSG RAN WG1 Meeting #93, Busan, Korea, May 21st – 25th, 2018.

[32] RP-180664, "NR-NTN: solution principles for NR to support non-terrestrial networks", Thales et al, 3GPP TSG RAN Meeting #80, La Jolla, USA, June 11th – 14th, 2018.

[33] R1-1806768 "Considerations on timing advance and random access for NTN", Nokia, Nokia Shanghai Bell, 3GPP TSG RAN WG1 Meeting #93, Busan, Korea, May 21st – 25th, 2018.

[34] ITU-R M.1225, "Guidelines for evaluation of radio transmission technologies for IMT-2000", 1997

[35] E. Lutz, M. Werner, and A. Jahn, "Satellite Systems for Personal and Broadband Communications", Berlin, Germany, Springer-Verlag, 2000.

[36] T. Rappaport, "Wireless Communications", New Jersey: Prentice Hall, 1996

[37] DVB Document A171-2, Digital Video Broadcasting (DVB) Implementation guidelines for the second generation system for Broadcasting, Interactive Services, News Gathering and other broadband satellite applications; Part 2 - S2 Extensions (DVB-S2X), March 2015.

[38] 3GPP TR 38.803 v14.2.0, "Study on new radio access technology: Radio Frequency (RF) and co-existence aspects".

[39] R1-1806750, "Considerations on random access for NTN", Samsung, 3GPP TSG RAN WG1 Meeting #93, Busan, Korea, May 21st – 25th, 2018.

[40] 3GPP TS 38.104, "Technical Specification Group Radio Access Network; NR; Base Station (BS) radio transmission and reception".

[41] R. Ali Ahmad, J. Lacan, F. Arnal, M. Gineste and L. Clarac, "Enhancing satellite system throughput using adaptive HARQ for delay tolerant services in mobile communications", 2015 Wireless Telecommunications Symposium (WTS), New York, NY, 2015, pp. 1-7.

[42] Tae Chul Hong, Kunseok Kang, Bon-Jun Ku, Dae-Ig Chang, "Receiver memory management method for HARQ in LTE-based satellite communication system", International Journal of Satellite Communications and Networking, 2017, 35, 1, 3.

[43] R1-1802613, "NTN NR impacts on the HARQ Operation", Fraunhofer, 3GPP TSG RAN1 meeting #92, Athens, Greece, Feb. 26 - Mar. 2, 2018.

[44] R1-1804857, "Deactivating HARQ for Non-Terrestrial Networks", InterDigital Inc, 3GPP TSG RAN WG1 Meeting #93, Busan, Korea, May 21st – 25th, 2018.

[45] R1-1805848, "Consideration on HARQ Impact for NTN", Nokia, Nokia Shanghai Bell, 3GPP TSG RAN WG1 Meeting #93, Busan, Korea, May 21st – 25th, 2018.

[46] O. Kodheli, A. Guidotti, and A. Vanelli-Coralli. "Integration of Satellites in 5G through LEO Constellations", CoRR abs/1706.06013 (2017): pp. 1-6.

[47] R1-1807164, "NR-NTN Channel Modeling – Flat fading criteria", THALES, 3GPP TSG RAN WG1 Meeting #93, Busan, Korea, May 21st – 25th, 2018.

[48] R1-1802551, "UE antenna assumption and beam modelling for NTN", Nokia, 3GPP TSG RAN WG1 Meeting #92, Athens, Greece, February 20th – March 2nd, 2018.

3.1 Definitions

For the purposes of the present document, the terms and definitions given in 3GPP TR 21.905 [1] and the following apply. A term defined in the present document takes precedence over the definition of the same term, if any, in 3GPP TR 21.905 [1].

Aerial: an airborne vehicle embarking a bent pipe payload or a regenerative payload telecommunication transmitter, typically at an altitude between 8 to 50 km.

Airborne vehicles: Unmanned Aircraft Systems (UAS) encompassing tethered UAS (TUA), Lighter than Air UAS (LTA), Heavier than Air UAS (HTA), all operating in altitudes typically between 8 and 50 km including High Altitude Platforms (HAPs)

Availability: % of time during which the RAN is available for the targeted communication. Unavailable communication for shorter period than [Y] ms shall not be counted. The RAN may contain several access network components among which an NTN to achieve multi-connectivity or link aggregation.

Beam throughput: data rate provided in a beam

Bentpipe payload: payload that changes the frequency carrier of the uplink RF signal, filters and amplifies it before transmitting it on the downlink

Connectivity: capability to establish and maintain data / voice / video transfer between networks and parts thereof

Geostationary Earth orbit: Circular orbit at 35,786 kilometres above the Earth's equator and following the direction of the Earth's rotation. An object in such an orbit has an orbital period equal to the Earth's rotational period and thus appears motionless, at a fixed position in the sky, to ground observers.

Low Earth Orbit: Orbit around the around Earth with an altitude between 500 kilometres (orbital period of about 88 minutes), and 2,000 kilometres (orbital period of about 127 minutes).

Medium Earth Orbit: region of space around the Earth above low Earth orbit and below geostationary Earth Orbit.

Mobile Services: a radiocommunication service between mobile and land stations, or between mobile stations

Mobile Satellite Services: A radiocommunication service between mobile earth stations and one or more space stations, or between space stations used by this service; or between mobile earth stations by means of one or more space stations

Non Geostationary Satellites: Satellites (LEO and MEO) orbiting around the Earth with a period that varies approximately between 1.5 hour and 10 hours. It is necessary to have a constellation of several Non Geostationary satellites associated with handover mechanisms to ensure a service continuity.

Non-terrestrial networks: Networks, or segments of networks, using an airborne or space-borne vehicle to embark a transmission equipment relay node or base station.

On Board processing: digital processing carried out on uplink RF signals aboard a satellite or an aerial.

One way latency: time required to propagate through the RAN from a terminal to the gateway or from the gateway to the terminal. This is especially used for voice and video conference applications.

Regenerative payload: payload that transforms and amplifies an uplink RF signal before transmitting it on the downlink. The transformation of the signal refers to digital processing that may include demodulation, decoding, re-encoding, re-modulation and/or filtering.

Relay node: Relay of Uu radio interface. The relay function can take place at Layer 1, 2 or 3.

Reliability: probability that the RAN performs in a satisfactory manner for a given period of time when used under specific operating conditions. The RAN may contain several access network components including an NTN to achieve multi-connectivity or link aggregation.

Round Trip Delay: time required for a network communication to travel from a terminal to the gateway or from the gateway to the terminal and back. This is especially used for web based applications.

Satellite: a space-borne vehicle embarking a bent pipe payload or a regenerative payload telecommunication transmitter, placed into Low-Earth Orbit (LEO) typically at an altitude between 500 km to 2000 km, Medium-Earth Orbit (MEO) typically at an altitude between 8000 to 20000 km, or Geostationary-satellite Earth Orbit (GEO) at 35 786 km altitude.

Space-borne vehicles: Satellites including Low Earth Orbiting (LEO) satellites, Medium Earth Orbiting (MEO) satellites, Geostationary Earth Orbiting (GEO) satellites as well as Highly Elliptical Orbiting (HEO) satellites

User Connectivity: capability to establish and maintain data / voice / video transfer between networks and Terminals

User Throughput: data rate provided to a terminal

3.2 Symbols

For the purposes of the present document, the following symbols apply:

<symbol> <Explanation>

3.3 Abbreviations

For the purposes of the present document, the abbreviations given in 3GPP TR 21.905 [1] and the following apply. An abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in 3GPP TR 21.905 [1].

2D two-dimensional

3D three-dimensional

ACM Adaptive Modulation and Coding

AMF Access and Mobility Management Function

AOA Azimuth angle Of Arrival

AOD Azimuth angle Of Departure

ARQ Automatic Repeat Request

AS Angular Spread

ASA Azimuth angle Spread of Arrival

ASD Azimuth angle Spread of Departure

AWGN Additive White Gaussian Noise

BLOS Beyond Line of Sight

BS Base Station

BW Bandwidth

C2 Control and Command

CDF Cumulative Distribution Function

CDL Cluster Delay Line

CFO Carrier Frequency Offset

CP Cyclic Prefix

CPE Common Phase Error

DS Delay Spread

EIRP Equivalent Isotropically Radiated Power

eMBB enhanced Mobile Broadband

FDM Frequency-Division Multiplexed

FOTA Firmware Over The Air services

FSS Fixed Satellite Services

GEO Geostationary Earth Orbiting

gNB next Generation Node B

GNSS Global Navigation Satellite System

GSO Geo Synchronous Orbit

GW Gateway

HAPS High Altitude Platform Station

HARQ Hybrid Automatic Repeat Request

HD High Definition

HEO Highly Elliptical Orbiting

ICI Inter-Carrier Interference

IoT Internet of Things

K Ricean K factor

KPI Key Performance Indicator

IMUX Input MUltipleXer

ISL Inter-Satellite Links

LEO Low Earth Orbiting

LMS Land Mobile Satellite

LOS Line of Sight

Mbps Mega bit per second

MEO Medium Earth Orbiting

mMTC massive Machine Type Communications

MS Mobile Services

MSS Mobile Satellite Services

NGSO Non Geostationary Satellite Orbit

NLOS Non-LOS

NT Non Terrestrial

NTN Non Terrestrial Network

O2I Outdoor-to-Indoor

OBO Output Backoff

OMUX Output MUltipleXer

PA Power Amplifier

PAPR Peak-to-Average Power Ratio

PL Path Loss

POI Point of Interest

PRACH Physical Random Access Channel

PSS Primary Synchronization Signal

RACH Random Access Channel

RAN Radio Access Network

RAR Random Access Response

RAT Radio Access Technology

RTT Round Trip Time

RRH Remote Radio Head

SCS Subcarrier Spacing

SIB System Information Block

SNR Signal-to-Noise Ratio

RMa Rural Macro

RMS Root Mean Square

Rx Receiver

SF Shadow Fading

SOTA Software Over The Air services

SSPA Solid-State Power Amplifier

SSS Secondary Synchronization Signal

TA Timing Advance

TAG Timing Advance Group

TDL Tapped Delay Line

TOA Time Of Arrival

Tx Transmitter

TV Television

UAS Unmanned Aerial System

UE User Equipment

UMa Urban Macro

UMi Urban Micro

URLLC Ultra-Reliable Low Latency Communications

VSAT Very Small Aperture Terminal

XPR Cross-Polarization Ratio

ZOA Zenith angle Of Arrival

ZOD Zenith angle Of Departure

ZSA Zenith angle Spread of Arrival

ZSD Zenith angle Spread of Departure

4.1 Roles for Non-Terrestrial Networks in 5G system

Thanks to the wide service coverage capabilities and reduced vulnerability of space/airborne vehicles to physical attacks and natural disasters, Non-Terrestrial Networks are expected to

- foster the roll out of 5G service in un-served areas that cannot be covered by terrestrial 5G network (isolated/remote areas, on board aircrafts or vessels) and underserved areas (e.g. sub-urban/rural areas) to upgrade the performance of limited terrestrial networks in cost effective manner,

- reinforce the 5G service reliability by providing service continuity for M2M/IoT devices or for passengers on board moving platforms (e.g. passenger vehicles-aircraft, ships, high speed trains, bus) or ensuring service availability anywhere especially for critical communications, future railway/maritime/aeronautical communications, and to

- enable 5G network scalability by providing efficient multicast/broadcast resources for data delivery towards the network edges or even user terminal.

The benefits relate to either Non-Terrestrial networks operating alone or to integrated terrestrial and Non-Terrestrial networks. They will impact coverage, user bandwidth, system capacity, service reliability or service availability, energy consumption, connection density (See [5]).

A role for Non-Terrestrial Network components in the 5G system is expected for the following verticals: transport, Public Safety, Media and Entertainment, eHealth, Energy, Agriculture, Finance, Automotive.

4.2 5G Use Cases wherein Non-Terrestrial Network components have a role

4.2.1 5G use cases introduction

A use case, typically refers to the interactions between a role and a system, to achieve a specific goal. Hence, it is necessary to identify the goal of the service enabled by a Non-Terrestrial network component integrated in the 5G system.

The tables in the clauses after respectively identify for each of the 5G service enablers, the use cases wherein Non-Terrestrial Network components have a role to play.

- 5G service enablers refer to eMBB (enhanced Mobile Broadband), URLLC (Ultra-Reliable Low Latency Communications) and mMTC (massive Machine Type Communications).

- 5G use cases correspond to the interactions between a stakeholder (user, operator, service provider) and the 5G system, to achieve a specific goal.

- The role of the Non-Terrestrial Network refers to services enabled by the Non-Terrestrial Network component in the 5G system to support the use case.

- 3GPP reference documents are provided in which the use cases are mentioned.

NOTE: While the propagation delay of satellite systems may be an issue for certain applications requiring ultra low latency, the importance of satellite for Critical Communications including public safety communications due to their dependability and large coverage area is well known.

Table 4.2.1-1: 5G use cases for Satellite access networks

Table 4.2.1-2: 5G use cases for Aerial access networks

4.3 Satellite and aerial access network architecture principles

Non-Terrestrial Network access typically features the following system elements:

- NTN Terminal: It may refer to directly the 3GPP UE or a terminal specific to the satellite system in case the satellite doesn't serve directly 3GPP UEs.

- A service link which refer to the radio link between the user equipment and the space/airborne platform. In addition the UE may also support a radio link with terrestrial based RAN.

- A space or an airborne platform embarking a payload which may implement either a bent-pipe or a regenerative payload configuration:

- A bent pipe payload: Radio Frequency filtering, Frequency conversion and amplification:

- A regenerative payload: Radio Frequency filtering, Frequency conversion and amplification as well as demodulation/decoding, switch and/or routing, coding/modulation. This is effectively equivalent to having base station functions (e.g. gNB) on board the space/airborne vehicle

- Inter satellite/aerial links in case of regenerative payload and a constellation of satellites. ISL may operate in RF frequency or optical bands

- Gateways that connect the satellite or aerial access network to the core network

- Feeder links which refer to the radio links between the Gateways and the space/airborne platform

We shall distinguish between two types of Satellite and Aerial access network

- Broadband access network serving Very Small Aperture Terminals that can be fixed or mounted on a moving platform (e.g. bus, train, vessel, aircraft, etc.). In this context, Broadband refers to at least 50 Mbps data rate and even up to several hundred Mbps (satellite) or even up to several Gbps (aerial) on the downlink. The service links operate in frequency bands allocated to satellite and aerial services (Fixed, Mobile) above 6 GHz.

- Narrow or wide band access network serving terminals equipped with Omni or semi directional antenna (e.g. handheld terminal). In this context, Narrowband  refers to less than 1 or 2 Mbps data rate on the downlink. The service links operate typically in frequency bands allocated to mobile satellite or aerial services below 6 GHz.

It is also helpful to distinguish between satellite and aerial systems with inter-satellite links (ISL) or inter-aerial links (IAL) and those without ISL/IAL.

For Aerial networks, we consider a configuration where base station functions are on board the airborne vehicle. The purpose of this network component is to provide the 5G service enablers to handheld devices.

Based on these principles, the figures below illustrate possible satellite and aerial access network architectures.

Figure 4.3-1: Satellite access network (without ISL) with a service link operating in frequency bands above 6 GHz allocated to Fixed and Mobile Satellite Services (FSS and MSS)

Figure 4.3-2: Satellite access network (with ISL) with a service link operating in frequency bands above the 6 GHz allocated to Fixed and Mobile Satellite Services (FSS and MSS)

Figure 4.3-3A: Satellite access network with a service link operating in frequency bands below 6 GHz allocated to Mobile Satellite Services (MSS)

Figure 4.3-3B: Satellite access network which service link operates below 6 GHz frequency bands allocated to Mobile Satellite Services (MSS) and complemented with the terrestrial access network served by the same or independent core networks.

Figure 4.3-4: Aerial access network (without IAL) with a service link operating in frequency bands below or above 6 GHz

Figure 4.3-4B: Aerial access network (with IAL) with a service link operating in frequency bands below or above 6 GHz

Figure 4.3-4C: Aerial access network (with IAL) with a service link operating in frequency bands above 6 GHz

It is recommended to select a range of deployment scenarios with either bent pipe or regenerative payloads. Note that the technical details of implementing the ISL interface is beyond the scope of this study.

4.4 Characteristics of NTN Terminals for satellite / aerial access network

Table 4.4-1 gives the minimum RF characteristics of the terminals operating respectively in Ka band (e.g. very small aperture terminals) and in S band (e.g. handheld terminals).

Table 4.4-1: Typical minimum RF characteristics of UE in satellite and aerial access networks

Note that other performance may be considered.

4.5 Air/Space borne vehicle characteristics

Table 4.5-1 provides characteristics of aerial and satellite vehicles that are relevant for the purpose of the study item:

Table 4.5-1: Typical characteristics of Airborne or Space-borne vehicles

The characteristics of the air/space-borne vehicles create specific Doppler and propagation delay conditions that NR has to cope with.

Table 4.5-2: Typical elevation angles in aerial and satellite based systems

4.6 Coverage pattern of NTN

Satellite or aerial vehicles typically generate several beams over a given area. The foot print of the beams are typically elliptic shape.

The beam footprint may be moving over the earth with the satellite or the aerial vehicle motion on its orbit. Alternatively, the beam foot print may be earth fixed, in such case some beam pointing mechanisms (mechanical or electronic steering feature) will compensate for the satellite or the aerial vehicle motion.

Table 4.6-1: Typical beam foot print size

Typical beam patterns of various NTN access networks are depicted below:

Figure 4.6-1: NTN Beam patterns

4.7 Non-Terrestrial Network architecture options

The possible options of NTN architecture in 5G context based on the RAN architecture principles described in [3] are shown below:

Figure 4.7-1: NTN featuring an access network serving UEs and based on a satellite/aerial with bent pipe payload and gNB on the ground (Satellite hub or gateway level)

In figure 4.7-1, the satellite or the aerial will relay a "Satellite friendly" NR signal between the gNB and the UEs in a transparent manner.

Figure 4.7-2: NTN featuring an access network serving UEs and based on a satellite/aerial with gNB on board

In figure 4.7-2, the satellite or the aerial includes full or part of a gNB to generate/receive a "Satellite friendly" NR signal to/from the UEs. This requires sufficient on board processing capabilities to be able to deploy gNB or Relay Node functions.

Figure 4.7-3: NTN featuring an access network serving Relay Nodes and based on a satellite/aerial with bent pipe payload

In figure 4.7-3, the satellite or the aerial will relay a "Satellite friendly" NR signal between the gNB and the Relay Nodes in a transparent manner.

Figure 4.7-4: NTN featuring an access network serving Relay Nodes and based on a satellite/aerial with gNB

In figure 4.7-4, the satellite or the aerial includes full or part of a gNB to generate/receive a "Satellite friendly" NR signal to/from the Relay Nodes. This requires sufficient on board processing capabilities to be able to deploy gNB or a Relay Node functionality.

NOTE: In the figures above a satellite represents both satellite and aerial platforms.

Table 4.7-1: 5G system elements mapping in NTN architecture

4.8 Spectrum

Satellite and Aerial systems operate in allocated frequency bands as per ITU-R/national allocation regime.

5.1 Scenarios overview

Based on the NTN overview background information presented in clause 4 and in examples of deployment scenarios, defined in the TR 38.913 [5] under clause 6.1.12 "Satellite extension to Terrestrial", the following Non-Terrestrial Network (NTN) reference deployment scenarios are down selected and will be further detailed in the study and used for the evaluations:

Table 5.1-1: Reference Non-Terrestrial Network Deployment scenarios to be considered in the NR-NTN study

The scenarios attributes used in the Table 5.1-1 are described below.

Only the main attributes are discussed in this clause, for simplification purposes. Complementary attributes that should be set up for each scenario are described in the clause 7.

The use cases mentioned in the Table 5.1-1, are described in clause 4.2.1.

5.2 Attributes

Platform orbit and altitude

This attribute stands for the Platform orbit type (GEO, Non-GEO) and its altitude.

A platform is either a satellite (alias space-borne vehicle), or a HAPS (airborne vehicle).

See clause 4.5 for further characteristics of Air / space borne vehicles.

Carrier frequency between air / space-borne platform and UE

The study addresses the whole frequency range between 0.5 – 100 GHz. For channel modelling and for the identification of areas of impact on the NR , the following frequency bands will be in particular considered:

- For VSAT, Ka band: Downlink: 19.7 - 21.2 GHz, Uplink: 29.5 – 30.0 GHz

- For UE, S band: Downlink: 2170 - 2200 MHz, Uplink: 1980 - 2010 MHz

The UE characteristics are described in clause 4.4.

Beam pattern

Beam pattern stands for "beam coverage pattern". It is described in clause 4.6.

Access scheme

For these scenarios, the FDD (Frequency Division Duplexing) is selected, versus TDD (Time Division Duplexing).

FDD means that the transmitter and the receiver operate at different carrier frequencies. Uplink and downlink sub-bands are separated by the named frequency offset.

Channel Bandwidth (DL + UL)

This scenario attribute stands for the available bandwidth for channels, for DL and for UL. It depends on the used carrier frequencies. For evaluation purposes, we will consider:

- For Satellite and aerial networks operating in frequency bands above 6 GHz, the bandwidth is up to 800MHz on both Downlink and Uplink

- For Satellite and aerial networks operating in frequency bands below 6 GHz, the bandwidth is up to 80MHz on both Downlink and Uplink

NTN architecture options

See clause 4.7.

NTN terminal type

For evaluation purposes:

- The VSAT transmit power will be set to 33dBm (2W), with a 60 cm equivalent aperture diameter (circular polarisation).

- For each 3GPP FDD power class (PC), the maximum output Power is: 33dBm (2W) for PC 1, 27dBm (0.5W) for PC 2 and 23dBm (0.20W) for the PC 3, with an omnidirectional antenna.  In a 1st approach and for evaluation purposes, the PC 3 UE will have a Transmit Power set to 23dBm (0.20W).

Relay node is defined in clause 3.1.

See clause 4.4 for further characteristics of UE of satellite / aerial access network.

NTN terminal distribution

This attribute is set to either:

- 100% outdoors UEs,

- 100% indoors UEs,

- Or mixed indoors & outdoors UE distribution

NTN terminal Speed

This attribute is a generic term relative to the transmitter/receiver which is on board the satellite or aerial platform. It stands for:

- High speed / low speed UE

- High speed / low speed platform (such as Trains, Boats embedding base stations )

For evaluation purposes, the selected maximum values are:

- 1000 km/h (e.g. aircraft)

- 500 km/h (e.g. high speed trains)

The effect of the maximum NTN terminal speed as well as satellite or aerial motion are considered in each deployment scenario.

See clause 4.5 for further characteristics on air / space borne platform.

5.3 Doppler and Propagation delay characterisation

5.3.1 Methodology

We shall distinguish between geostationary satellite, non geo stationary satellite and HAPS platforms.

5.3.1.1 Propagation delay

We consider the one way propagation delay as the delay:

- from the Gateway to the UE via the space/airborne platform (bent pipe payload)

- from the space/airborne platform to the UE (regenerative payload)

The Round Trip Time corresponds to the two way propagation delay:

- from the Gateway to the UE via the space/airborne platform and return (bent pipe payload)

- from the space/airborne platform to the UE and return (regenerative payload)

For the propagation delay analysis, we consider a minimum gateway elevation angle of 5° (the elevation angle of the space/air borne platform from the Gateway). While the minimum terminal elevation angle is typically 10°.

The actual propagation delay depends on the space/airborne platform altitude and respective position of the gateway and terminal.

5.3.1.2 Differential delay

The differential delay corresponds to the difference of propagation delays between two chosen points that are at some specific positions within the beam foot print: for example the points can be selected at nadir and Edge of Coverage.

The path to gateway is likely to be the same for all terminals, but this just to simplify the computation.

5.3.1.3 Doppler shift/variation

Doppler shift: Shift of the signal frequency due to the motion of the receiver, the transmitter or both.

Doppler variation rate: During time, the Doppler shift is evolving. This is called the Doppler variation rate or simply Doppler rate.

The Doppler shift and Doppler variation depend on the relative speed of the space/airborne platforms, the speed of the UE, and the carrier frequency.

The figure below recalls the basic geometry of the system. The carrier frequency of the signal received at satellite is affected by the motion of the transmitter. The Doppler on the signal received by the UE from the satellite is also impacted by the motion of the UE in addition to the motion of the satellite or HAPS. Since both the air/spaceborne vehicle and the UE are moving relatively to the Earth, their respective effects can be added algebraically.

In the present document, we can follow a non-relativistic approach to compute the Doppler shift and variation rate given that the ratio between the relative speed of the transmitter or receiver and the light velocity is negligible.

- For a terminal at a speed of 1000 km/h (or 0.277 km/s): this ratio is 0.277/300000 = 0.00009

- For a relative speed of Non-Geo satellite of 7.5 km/s (orbital speed): the ratio is 0.000025

The signal received by the satellite at a nominal carrier frequency Fo is affected by a Doppler shift.

The Doppler shift is computed with the formula:

Doppler shift formula: ∆F = Fo*V* cos (θ)/c

Where

- Fo: nominal carrier frequency

- V = UE velocity

- Θ is the angle between the velocity vector V of the mobile (Transmitter or receiver ) and the direction of propagation of the signal between the UE and the space/airborne platform.

Figure 5.3.1.3-1: Definition of the theta angle between space/airborne platform and the direction of the UE in motion

When a transmitter is moving away from a receiver, ∆F is negative.

When a transmitter is moving towards a receiver, ∆F is positive.

The Doppler shift variation corresponds to the variation of the Doppler shift over time. In other words, it refers to the derivative of the Doppler shift function of time.

5.3.2 Geo-stationary platforms

Geostationary platform are orbiting at 35786 km altitude in the equatorial plan, and is fixed with respect to the earth. Nevertheless, due to some imperfection of the terrestrial potential, the satellite has some motion around its orbital position, as described in a further section.

5.3.2.1 Propagation delay

One should distinguish between

- Bent pipe payloads

- One way propagation delay is the sum of feeder link propagation delay and user link propagation delay, thus the propagation delay between Gateway and UE via the satellite

- Round Trip Time is the delay over the path, Gateway-Satellite-UE-Satellite-Gateway. It corresponds to twice the one way propagation delay

- Regenerative payloads (decoding/coding on board)

- One way propagation delay is the propagation delay between the satellite and the UE

- Round Trip Time is the delay over path: satellite-UE-satellite

In both cases the transit time and/or processing time are not taken into account.

For the propagation delay computation, the min elevation angle is set at 5° for the Gateway, and is set at 10°for the terminal can be set at various elevation angles, but we consider that the worst case is 10° elevation angle.

The following table summarises the different situation and the different distances in km and the different propagation delays in ms.

Table 5.3.2.1-1: Propagation delays for GEO satellite at 35786 km

5.3.2.2 Differential delay

In this clause, we compute the differential delays between specific positions: for instance at nadir and Edge of Coverage.

The path to gateway is supposed to be the same for all UEs.

Table 5.3.2.2-1: Differential Delay for GEO satellite

For Geostationary satellites we have also taken a satellite located at 10 ° E and we have computed different differential delays between some points, provided all points were linked to the same Gateway.

The table is valid for both bent pipe satellite and regenerative satellite.

Table 5.3.2.2-2: Differential delay examples

5.3.2.3 Doppler shift

In principle, the Geostationary satellite is fixed and therefore no Doppler shift is induced except that due to possible UE motion.

In reality the satellite is moving around its nominal orbital position, due to perturbations (e.g. sun, moon) and to non-spherical component earth attraction which impact the earth gravitational force.

The satellite must be kept to inside a box described here below. The satellite is typically maintained inside a box that has the following dimensions, by thrust or plasmic propulsion.

Figure 5.3.2.3-1: Trajectory box for a Geostationary satellite

Without maintaining the satellite inside the box, the motion could be a higher value like inclination up to +/6 °.

We take the hypothesis that the satellite is kept in the limited box. The trajectory that the satellite follows is an "8" as shown in next figure. The plane is seen from the centre of the Earth. The blue arrows in the next figure indicate the sense of motion of the satellite around its orbital position So.

Figure 5.3.2.3-2: Geostationary satellite trajectory

In the figure above, the trajectory of the satellite is represented as seen from a point at the equator having same longitude as the nominal Geostationary satellite orbital position.

A geostationary satellite will cover the whole trajectory in 24 Hours.

The average tangential velocity of a geostationary satellite with respect to an earth point is around 2.74 m/s.

Satellite maintained in a typical trajectory box (see figure 2) characterized by

- +/- 37.5 km in both latitude and longitude directions corresponding to an aperture angle of +/- 0.05 °.

- +/- 17.5 km in the equatorial plane.

To illustrate the Doppler shift computation using the Doppler Shift formula, we shall consider some concrete cases:

- Geostationary Satellite at 10 ° E (over Europe)

- First a High Speed Train (500 km/h) from Paris to Lille (France) and from Paris to Strasbourg (France)

- Secondly an air plane (1000 km/h and 10 km altitude) moving in the same directions.

We first compute the Doppler shift while supposing the satellite has no motion, but on a moving UE, and secondly we evaluate the impact of the satellite motion on a fixed UE.

First case: Satellite is considered fixed with respect to earth point

In the high speed train going north from Paris the obtained Doppler shift is provided here below

Table 5.3.2.3-1: Examples of Doppler shift with GEO and a terminal on board a High Speed Train in opposition direction

Table 5.3.2.3-2: Example of Doppler shift with GEO and a terminal on board an aircraft in opposition direction

And going from Paris to east.

Table 5.3.2.3-3: Example of Doppler shift with GEO and in High Speed Train

Table 5.3.2.3-4: Example of Doppler shift with GEO and in a plane

The Doppler shift is highest for a platform moving along longitude compared to a moving platform along latitude.

In the figure below, we consider a train travelling North from the Equator at a constant speed of 500 km/h. The two extreme points in the figure are 3600 seconds apart. The Doppler shift plotted as a function of the latitude. The maximum rate of change of Doppler shift is approximately -23 mHz/s

Figure 5.3.2.3-3: Doppler Shift at 2 GHz for a High Speed Train travelling along a longitude (North direction)

In the figure below, we consider an aircraft travelling North from the Equator at a constant speed of 1000 km/h. Similarly to the previous plot, the two extreme points are 1800 seconds apart. The Doppler shift plotted as a function of the latitude. The maximum rate of change of Doppler shift is approximately -90 mHz/s.

Figure 5.3.2.3-4: Doppler Shift at 2 GHz for an aircraft travelling north

However these values are reached only when cos (θ) is equal to 1 or -1. Where θ is the angle between the vector speed and the direction of wave propagation (the axis UE-Satellite).

Second case: Satellite is moving on its "8"

When satellite is moving from S2 to S1, the Doppler shift in Paris is the following

Table 5.3.2.3-4:Example of Doppler shift when satellite is moving

When satellite is moving from S1 to S4, the Doppler shift in Paris is the following

Table 5.3.2.3-5:Example of Doppler shift when satellite is moving

Doppler shift is higher than in the previous case, though still very low compared to the case of Non GEO satellites.

When satellite is in near GEO orbit with inclination up to 6°, the Doppler shift can reach around 300 Hz at 2 GHz, then 3000 Hz at 20 GHz and 4500 Hz at 30 GHz, which are still compatible with OFDM.

5.3.3 Aerial vehicle

The altitude of aerial vehicle also called UAS (Unmanned Aircraft Systems) can be between 8 and 50 km, including HAPS. HAPS is a station located on an aerial object at an altitude of 20  to 50 km and at a specified, nominal, fixed point relative to the Earth.

The general UAS based system architectures are presented in the following picture.

Figure 5.3.3-1: UAS based system architectures

The coverage can be divided into small cells, and usually the minimum elevation angle for a Mobile Terminal is 5°.

The platform can move around its nominal position within a few kilometres at a maximum tangential velocity of 15 m/s.

This can result in maximum Doppler shift (in absolute value) of 100 Hz @ 2GHz, 1000 Hz @ 20 GHz and 1500 Hz @ 30 GHz due to Haps motion.

In S band, at 100 km/h a car will suffer a Doppler shift of +/- 185 Hz maximum

The Doppler variation can be evaluated with a car moving from one edge to another at 100 km/h , covering 450 km . The Doppler variation will be around -0.0025 Hz/s. So no impact on demodulation

At 5° elevation angle the distance to the aerial vehicle is 229 km, and if we suppose the Gateway is at same distance

- One way delay is around 1.526 ms

- Round Trip Time is 3.053 ms

- Differential delay between nadir and Edge of Coverage: 0.697 ms

5.3.4 Non geostationary satellites

The Non-Geostationary case comprises three examples

- LEO  at 600 km

- LEO at 1500 km

- MEO at 10000 km

5.3.4.1 Propagation delay

In the case of bent pipe satellites, one way propagation delay is the sum of feeder link propagation delay and user link propagation delay, thus the propagation delay between Gateway and UE.

In the case of regenerative satellite, one way propagation delay is the satellite to UE propagation delay.

In both cases the transit time and/or processing time are not taken into account.

In the case of bent pipe satellite, the Round Trip Time is the physical path duration of the path : Gateway-Satellite-UE-Satellite-Gateway, that is in fact twice the one way propagation delay.

In the case of regenerative satellite, the round trip delay is the delay corresponding to the following path :satellite-UE-satellite.

In the computation, Gateway is set at 5° (TBC) elevation angle, and terminal can be set at various elevation angles, but we consider that the reference case is 10° elevation angle for the propagation delay computation.

The following table summarises the different situations and the different distances in km and the different propagation delays in ms.

The results for the three cases of NGSO satellites are summarized in the next table.

Table 5.3.4.1-1: Propagation delays for different NGSO satellites (altitude and payload types)

5.3.4.2 Differential delay

In this clause, we compute the differential delays between some specific positions : for instance at nadir and Edge of Coverage.

The path to gateway is supposed to be the same for all terminals.

Table 5.3.4.2-1: Differential Delay for LEO satellite

5.3.4.3 Doppler Shift and variation rate

The following picture summarizes the methodology used for Non Geostationary systems. We evaluate the Doppler shift which is maximum when the UE is located in the orbital plane.

Figure 5.3.4.3-1: System Geometry for Doppler computation

The picture describing the system geometry shows the satellite "S" on its circular orbit. The vector V corresponds to the orbital speed vector.

The Doppler shift is computed for a Mobile Terminal "M" located in the orbital plan, and corresponds to the maximum value.

One of the impacting factors on the Doppler shift value is the angle between and the speed vector . Angle called θ.

- The satellite is at an altitude h, and R is the earth radius.

- The satellite has the velocity , and the transmitted frequency is Fc.

- The Doppler shift value Fd  due to satellite motion is expressed by the formula

- 

- Where

- θ is the angle between satellite velocity and .

- u the angle between and

-  is the vector between earth centre and point on earth

- is the vector between earth centre and the satellite

- angle u is varying with the satellite motion: u(t) = V*t/(R+h) with t the time

- α is the elevation angle to the satellite of the UT in M.

- γ can be computed as follow:

- 

- The Doppler formula is obtained after some computation.

At this altitude the speed of the satellite in circular orbit is 7.5622 km.s-1. So we can use non-relativistic approximation to compute Doppler shift.

Also at first order we neglect the speed of earth which is 327 m/s at 45° latitude and 464 m/s at the equator.

For all Non GSO cases, the satellite speeds are the following

- At 600 km : V =7.5622 km.s-1

- At 1500 km : V =7.1172 km.s-1

- At 10000 km : V =4.9301 km.s-1

5.3.4.3.1 Case at 2 GHz

Both (Downlink) D/L and (Uplink)  U/L the signal is around 2GHz and we limit the curves at 2 GHz.

If we consider now a moving UE at 1000 km/h, and moving in the same direction than the satellite, we have determined the worst case impact in the following graph. We can define the bounds by adding the Doppler shift due to the satellite motion and the Doppler shift due to the UE motion.

All the curves are gathered in the next graphs, showing clearly the boundaries of the Doppler shift depending on the sense of motion between the satellites and the UE.

Three NON GSO satellites cases are provided.

Figure 5.3.4.3.1-1: Case with 2 GHz signal at 600 km on D/L and U/L: fixed UE and UE in motion

Figure 5.3.4.3.1-2: Case with 2 GHz signal at 1500 km: fixed UE and UE in motion

Figure 5.3.4.3.1-3: Case with 2 GHz signal at 10000 km: fixed UE and UE in motion

5.3.4.3.2 Case in Ka band

There are two cases

- Downlink at 20 GHz

- Uplink at 30 GHz

If we consider now a moving UE at 1000 km/h, and moving in the same direction than the satellite, we have determined the worst case impact in the following graph.

This impact is at maximum 18 kHz in one sense or the other at 20 GHz, and 27 kHz at 30 GHz, all the curves are gathered in the next graph, showing clearly the boundaries of the Doppler shift depending on the sense of motion between the satellite and the UE.

Figure 5.3.4.3.2-1: Case with 20 GHz signal at 600 km on D/L: fixed UE and UE in motion

Figure 5.3.4.3.2-2 Case with 30 GHz signal at 600 km on D/L: fixed UE and UE in motion

Figure 5.3.4.3.2-3: Case with 20 GHz signal at 1500 km on D/L: fixed UE and UE in motion

Figure 5.3.4.3.2-4: Case with 30 GHz signal at 1500 km on D/L: fixed UE and UE in motion

Figure 5.3.4.3.2-5: Case with 20 GHz signal at 10000 km on D/L: fixed UE and UE in motion

Figure 5.3.4.3.2-6: Case with 30 GHz signal at 10000 km on D/L: fixed UE and UE in motion

The different cases are summarized here below with the ratio of maximum Doppler shift in absolute value to the central frequency.

Table 5.3.4.3.2-7: Summary of Doppler shift and shift variation for different altitudes

Note that the Maximum Doppler shift variation in absolute value is always negative and observed when the Doppler shift is zero.

5.3.4.4 Doppler Shift and variation rate

The following picture summarizes the methodology used to compute Doppler shift for Non Geostationary satellite systems. It assumes a Cartesian coordinate system such that the moving satellite and the receiver are on the y-z plane. The Doppler shift experienced by a stationary receiver can be computed as follows as a function of time:

where f0 is the carrier frequency, d(t) is the distance vector between the satellite and the receiver, and xSAT(t) is the vector of the satellite position. These vectors can be expressed as:

where RE is the Earth radius, h is the satellite altitude, and is the satellite angular velocity.

Figure 5.3.4.4-1: System geometry for Doppler computation (Satellite moves in the Y-Z plane)

After some mathematical manipulation [7], the Doppler shift as a function of the elevation angle is computed in a closed-form expression as follows:

where the angular velocity is , with G the gravitational constant and ME the Earth mass.

If the receiver is placed on board an aircraft or a high speed train, there will be an additional term of Doppler shift resulting from its own velocity. In case of Non Geostationary satellites, the Doppler shift due to satellite movement is much higher than the one caused by UE movement. For GEO and HAPS, the Doppler shift component is mainly caused by the UE movement.

5.3.5 Synthesis for each scenarios

Following table summarises the different Doppler shift, Doppler Shift variation and propagation delays. The main impairments are the Doppler shifts and Doppler variation in deployment scenarios D3 and D4. (Non-geostationary platforms at 600 km).

Table 5.3.5-1: Summary of Doppler shift, Doppler Shift variation and propagation delay for LEO at 600 km, GEO and HAPS

NOTE : In some cases like UE on board an aircraft during taking off, the acceleration can add a supplementary Doppler variation in absolute value of respectively 262 Hz/s @ 20 Ghz, and 393 Hz/s @ 30 GHz.

6.1. Status/expectation of existing information for satellite/HAPS channels

6.1.1 Channel modeling works outside of 3GPP

ITU recommendations are encompassing most recent works and measurements on satellite channel models.

- ITU-R P.681 [10] defines the Land Mobile Satellite channel with measurements up to 20 GHz

- ITU-R P.618 [11] describes atmospheric effects such as gas attenuation, scintillation, rain and cloud attenuation.

6.1.2 Targeted user environment

Only outdoor conditions are considered for satellite operations, since performance requirements are not expected to be met with the available link budget for indoor communications.

Since HAPS are closer to the Earth, resulting in less path loss than in satellite access networks, additional indoor conditions are also considered for HAPS.

Several user environments will be considered, depending on the frequency band: open, rural, suburban, urban and dense urban. In open environments (such as fixed terminals or terminals mounted on boats/aircrafts), an AWGN channel is assumed.

6.1.3 Modeling objectives

The requirements for channel modelling are as follows:

- Support a frequency range from 0.5 GHz up to 100 GHz. Two frequency bands are targeted in particular: below 6 GHz and Ka bands. For Ka band communications, the uplink frequency is around 30 GHz while the downlink frequency is around 20 GHz.

- Accommodate UE mobility. For satellite channel models, mobility speed up to 1000 km/h is supported; this corresponds to aircrafts that can be served by satellite access. For HAPS channel models, mobility speed up to around 500 km/h is supported, corresponding to high speed trains.

6.2 Differences between satellite/HAPS and cellular channel modelling

Figures 6.2-1 and 6.2-2 compare the macro-cellular and satellite access links in NLOS and LOS cases, respectively. The terrestrial propagation is quite similar: multipath propagation is caused by objects near the user. However, the angular spread from satellite is almost zero (due to its distant location) while it can still be several degrees from the base station.

Figure 6.2-1: Macro-cellular vs. satellite channel, NLOS

Figure 6.2-2: Macro-cellular vs. satellite channel, LOS

Figure 6.2-3: Combined satellite and terrestrial channels (conceptual drawing).

6.3 Coordinate system

A three-dimensional global coordinate system is considered, described as "Earth Centred Earth fixed". The Earth is approximated as a true sphere with radius of 6371 km. The coordinates' origin O lies in the center of the earth, x-y plane locates in the equator plane with x-axis pointing to 0 degree longitude, y axis pointing to 90 degree longitude, and z-axis pointing to geographical north pole from the origin O.

A UE or a satellite position is described by a set of three parameters, with for all UEs and for all satellites.

The proposed coordinate system is illustrated in Figure 6.3-1 for a non-GEO satellite constellation.

Figure 6.3-1: Illustration of the coordinate system

6.4 Antenna modelling

6.4.1 HAPS/Satellite antenna

Satellite antenna pattern

The following normalized antenna gain pattern, corresponding to a typical reflector antenna with a circular aperture, is considered

 1 

where J1(x) is the Bessel function of the first kind and first order with argument x, is the radius of the antenna's circular aperture, k = 2f/c is the wave number, f is the frequency of operation, c is the speed of light in a vacuum and  is the angle measured from the bore sight of the antenna's main beam. Note that ka equals to the number of wavelengths on the circumference of the aperture and is independent of the operating frequency.

The normalized gain pattern for a = 10 c/f (aperture radius of 10 wavelengths) is shown in Figure 6.4.1-1.

Figure 6.4.1-1: Satellite antenna gain pattern for aperture radius 10 wavelengths, a=10 c/f

HAPS antenna pattern

Two different antenna patterns are considered:

- The above antenna pattern defined for satellite scenarios, based on the Bessel function.

- The 3GPP antenna pattern defined for the base station in Section 7.3 of [12], corresponding to a uniform rectangular panel array with dual linear polarization.

6.4.2 UE antenna pattern

The following reference UE antenna patterns are adopted for fast fading:

- Quasi Isotropic - Linear polarisation (Quasi isotropic refers to dipole antenna which is omni-directional in one plane)

- Co-phased array - Dual Linear polarisation (one for below 6 GHz band and one for above 6 GHz band as described in [48])

- "VSAT type - circular polarization: fixed or tracking" UE antenna pattern (only in deployment scenarios featuring flat fading conditions)

6.5 Methodology to define channel models

6.5.1 System-level methodology

Only drop-based simulations are considered, similarly to [12].

The baseline model to generate channel coefficients is the one described in [12] for terrestrial links, and depicted in Figure 6.5.1-1.

Figure 6.5.1-1: Channel coefficient generation procedure issued from [12]

An alternative and simplified model can be applied if all UE meet the flat fading criteria. In this case, the channel coefficients reduce to a single tap, since the channel is not frequency selective. This simplified model, derived from [10] is depicted in Figure 6.5.1-2.

Figure 6.5.1-2: Simplified channel coefficient generation issued from [10]

6.5.2 Link-level methodology

Similarly to [12], reference CDL and TDL are considered for link-level simulations. For given environment and elevation angle, they are obtained from a single instance of the baseline model used for system level simulations (i.e. the one derived from [12]).

For flat fading conditions (including AWGN) no channel model is needed for link-level simulations.

6.6 Large scale model

6.6.1 LOS probability

Line-Of-Sight (LOS) probability depends on UE environment and elevation angle, and is obtained from Table 6.6.1-1. Reference elevation angles are considered from 10° to 90° with a 10° step. For an UE-to-satellite or UE-to-HAPS link, the LOS probability is taken from the nearest reference elevation angle.

Table 6.6.1-1 LOS probability

6.6.2 Path loss and Shadow fading

The signal path between a satellite or HAPS transmitter and an NTN terminal undergoes several stages of propagation and attenuation. The path loss (PL) is composed of components as follows:

 , (6.6-1)

where is the total path loss in dB,

  is the basic path loss in dB,

  is the attenuation due to atmospheric gasses in dB,

  is the attenuation due to either ionospheric or tropospheric scintillation in dB,

 is building entry loss in dB.

This section specifies the basic path loss model () which accounts for the signal's free space propagation, clutter loss, and shadow fading. Attenuations due to building entry loss, atmospheric gasses and scintillation are described in Sections 6.6.3, 6.6.4 and 6.6.6, respectively.

The free space path loss (FSPL) in dB for a separation distance d in meter and frequency in GHz is given by

  (6.6-2)

For a ground terminal, the distance d (a.k.a. slant range), as shown in Figure 6.6.2-1, can be determined by the satellite/HAPS altitude and elevation angle α by

 , (6.6-3)

where denotes Earth radius.

Figure 6.6.2-1: Slant range d between a satellite and a ground terminal

Clutter loss (CL) models the attenuation of signal power caused by surrounding buildings and objects on the ground. It depends on the elevation angle α, the carrier frequency fc, and the environment. Shadow fading (SF) is modeled by a log-normal distribution, which when expressed in decibel unit, is a zero-mean normal distribution with a standard deviation , i.e., .

The basic path loss in dB unit is modeled as

 , (6.6-4)

where is the free space path loss, is clutter loss, and is shadow fading loss represented by a random number generated by the normal distribution, i.e., ~. When the UE is in LOS condition, clutter loss is negligible and should be set to 0 dB in the basic path loss model.

The values of and are given in tables 6.6.2-1 to 6.6.2-3 at reference elevation angles for different scenarios. The UE in a particular scenario should take the values corresponding to the reference angle nearest to its elevation angle α.

Table 6.6.2-1: Shadow fading and clutter loss for dense urban scenario

Table 6.6.2-2: Shadow fading and clutter loss for urban scenario